An Ocean Meets a River
Saltwater inlet or freshwater river? As an estuary, the Hillsborough is both. Atlantic Ocean tides reach three-quarters of the way to the river's headwaters, while inland streams and tributaries feed its upper stretch. Seawater pushing in is diluted by freshwater draining out, creating a modified marine environment that supports a highly specialized ecosystem.

Saltwater Wedge: In the estuary, mixing of saltwater and freshwater is not always uniform. Under flood tide conditions, tidal waters coming into contact with freshwater cause denser saltwater to sink to the bottom, and the freshwater to rise, forming a saltwater "wedge." The wedge is narrow at the head of the river, but broadens out towards the mouth. Mixing may also occur as the result of:
• high winds
• changing water temperatures
• other factors which influence the velocity and direction of the currents.

A Fine Balance: The degree of salinity in the Hillsborough River has determined both its ecological and economic fate. Just right for oysters, but too fresh for their main predator — starfish — the river is home to a thriving commercial oyster fishery. It is also prime habitat for several species of anadromous fish that return from the sea to spawn in freshwater or low salinity areas of the river.

Saltmarsh Specialties
Alternately bathed in saltwater tides, then exposed to sun and wind, the grassy tidal flats of the Hillsborough River have developed into a rich, highly adaptable natural environment. Salt-tolerant spartina grasses line the shore, anchoring a diverse aquatic and terrestrial ecosystem that performs several important functions:
• Fish rearing - Wetland areas act as a nursery for many fish, including striped bass, gaspereau, smelts and shellfish.
• Wildlife habitats - Shorebirds, waterfowl, waders, songbirds and birds of prey, as well as red foxes, raccoons, weasels, mink, skunks and coyotes breed and feed in the buffer between farmland, woodland and water.
• Filtration - The saltmarsh transition zone between the river and the land settles out soil particles and other matter into its mud flats. Organic matter is broken down and recycled, then redistributed by flushing tides.

Encouraging Reforestation
Centuries ago, the banks of the Hillsborough were lined with the old-growth species such as beech, sugar maple, yellow birch, white pine, red oak and Eastern hemlock in what is now known as the Acadian Forest. Settlement, farming, saw milling, shipbuilding and even leather tanning (using the tannin of Eastern hemlock bark) eliminated most of the old growth woodlands.

Woodland Appreciation: Today, woodlands are regenerating, and just over one-third of the Hillsborough watershed is forested. Younger species, such as old field white spruce and bog-loving black spruce, are most common. Local land management and conservation groups are now recognizing the need to encourage riparian reforestation, species diversity and protection of wildlife habitat. A Demonstration Woodlot in Auburn and the Royalty Oaks Natural Area, a 4 hectare stand of mature red oaks in East Royalty, have been established to promote woodland appreciation.